Combine Bone-in, Skin-on Chicken Thigh (3 pound), chopped Onion (2), chopped Carrot (2), chopped Celery (3 stalk), chopped Tomato (1), Mushroom (8 ounce), Fresh Thyme (4 sprig), Bay Leaf (1), Fresh Parsley (1 bunch), Salt (1 dash), whole Peppercorns (1 teaspoon), and Water (8 cup).
Cover and cook on low for 8-9 hours or on high for 4-5 hours in a 6-quart slow cooker, until the broth is deeply flavored.
Let the broth settle for 5 minutes and remove as much fat as possible from the surface using a large spoon. Remove the solids.
Strain the broth through a fine-mesh strainer into a large container. Refrigerate or freeze it for later.